text:
What missile defense systems would be used against hypersonic glide vehicles?

What missile defense systems would be used against hypersonic glide vehicles and cruise missiles (like Avangard or Sky Star)? What challenges would nations face developing them?

I think you're pushing the limits of what's on topic here. This doesn't fit within the topics covered in the [help/on-topic]

The conventional approach is to simply nuke it. The issue here is not really about speed but its maneuveribiliry. Ballistic missiles have similar speeds but its feasible to intercept because the trajectory is predictable. When the target can dodge your interceptor vehicle its totally different game.

From an aeronautical point of view, an interceptor normally must be faster than the target it is seeking to reach. Therefore, existing missile defense systems are ineffective against hypersonic aircraft, because the target is moving at least as fast as the would-be interceptor.
Of course, if the target moves in a unchanging straight line, then it is theoretically possible for the interceptor to reach it, so long as it is positioned in front of the target. For this exact reason, all hypersonic missiles are designed to make irregular movements in any situation where an interceptor may be present.
For straight line paths, there is a cone of viability where an interceptor needs to be in order to intercept the target. The slower the interceptor is, the smaller this cone becomes. In the current (2020) strategic situation, the cone of intercept for existing hypersonic weapons is so small that the probability of intercept is impractically small, even for high value targets. This is one reason why there is a great effort currently to develop laser-based defensive systems.

Patriot missiles have a stated range of 35km against ballistic missiles, which are hypersonic during reentry. The PAC-3 is capable of Mach 4+. The THAAD missile is capable of Mach 8+.

@RalphJ Well, those are just maximum speeds during endgame, not cruising speeds. Furthermore, the fire control systems for those missiles assume the target is moving in a predictable trajectory, which is not true for a glide missile.

@RalphJ Do you think THAAD or PAC-3 could take out a hypersonic glide body?

Nike missiles on patrolling B36 (6) or B52 (4).  Would save several seconds.  The real question would be if it can be tracked before re-entry.  It will be a meteor once it heats up.


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What is the best major to study for a career in propulsion systems design?
I want to be an aerospace engineer but am not sure what to major in. I really want to design propulsion systems. What would be the best major for this and what could I do to increase my chances of being hired?

This sort of question isn't a great fit for this site because there are too many variables and ultimately it comes down to opinions. You might get a better response in a discussion forum where you can get a range of opinion, and people can ask follow-up questions.

To add to what Pondlife said, it is really dependent on what majors are available (extreme example: I bet there are majors in aircraft propulsion systems somewhere). So this can never be a straightforward Q&A because it's very much specific to your situation.

If you mean gas turbines, metallurgical engineering would not be a bad choice as much of turbine technology depends on materials.  My old school happens to have combined aerospace and metallurgy into a single degree.

While the question is certainly subjective, I wanted to help you out as much as possible. I spoke to a friend who works as an electrical engineer at NASA and asked him your question. Based on his advice and some of my own research on your behalf, the most direct route would be to pursue an aerospace engineering degree in a good university program - CIT, MIT, UM Ann Arbor, etc. (there are plenty of schools to choose from). Most aerospace engineering students will choose a specialty in either an area of design or even in a specific type of vehicle - many universities will allow you to specialize in propulsion - essentially tailoring your electives to include subjects like fluid dynamics, multivariate and non-linear controls, combustive thermodynamics, and turbomachinery. That said, my friend indicated that the field can be very competitive, and that many propulsion system designers probably did not begin their career doing that kind of work. Be prepared to be flexible and plan on playing the long game when it comes to reaching your dream job. Also, as is the case in any competitive industry, networking can be key. Be sure to find opportunities to meet people in your field, ask questions, and get to know others who can give you the inside track on openings and opportunities.
Hope this helps.

Thank you so much.

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What do a "sheared pump drive" and a "possible sticky vacuum regulator" mean?
The POH for a PA28 (engine driven vacuum pump) says a decrease in pressure on the gyro suction gauge may indicate a possible sticky vacuum regulator. A zero pressure indication means a sheared pump drive. What exactly does that mean?

There is a small vacuum pump attached to the engine by a small rotating shaft which generates vacuum whenever the engine is running. That vacuum is used to spin up the gyro instruments in the plane.
Because the pump produces different amounts of vacuum at different engine speeds, its vacuum output must be sent through a device called a regulator to furnish a constant vacuum to the instruments at all times.
If the vacuum pump drive shaft is broken ("sheared"), the pump produces no vacuum and the gyros go dead- and the suction gauge reads no suction. If the regulator mechanism is stuck or jammed, it stops working as a regulator and allows full suction pressure to be applied to the instruments- and the suction gauge reads too much suction.

Do you know if the gauge is before or after the regulator?

Good answer, I'd just add that the regulator can get stuck the other way, giving too little suction.

The gauge is after the regulator @Dan, you are seeing the regulated pressure as that's what the instruments see.

I wonder if the pump drive shaft is intentionally designed to shear easily, to prevent affecting the engine in case of a malfunction.

Those vane suction pumps are not very reliable because the vanes are made of carbon and are brittle.  The vanes break apart and jam the pump, and shear the drive.  Also, there is a filter on the inlet side of the system, prior to the vacuum instruments.  If it's clogged more than the regulator can accommodate, it can result in a excessively high vacuum indication due to the restriction.

Another thing that result in low suction is a vacuum system leak.  Vacuum pumps are life limited, and in many cases, especially if reliability is required such as for IFR flying, many operators and owners will replace the vacuum pump every 500 hours as a preventive maintenance measure.

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Is there a list of airports with Category 3 ILS systems?
Is there a list of airports with category 3 Instrument Landing Systems?

According to my current navigation database (AIRAC 1912), the following 228 airports have a category III ILS approach to at least one of their runways:
CYVR (VANCOUVER INTL) on runways: 08L, 08R, 26L, 26R
CYYC (YYC CALGARY INTL) on runways: 17L, 35R
CYYT (ST JOHNS INTL) on runways: 11, 29
CYYZ (LESTER B PEARSON INT) on runways: 05, 06L
EBBR (BRUSSELS NATIONAL) on runways: 25L, 25R
EBCI (BRUSSELS SOUTH) on runway: 24
EBLG (LIEGE) on runways: 04R, 22L
EDDB (SCHOENEFELD) on ALL runways: 07L, 25R
EDDC (DRESDEN) on runway: 22
EDDE (ERFURT-WEIMAR) on runway: 28
EDDF (FRANKFURT/MAIN) on runways: 07C, 07L, 07R, 25C, 25L, 25R
EDDG (MUENSTER/OSNABRUECK) on runway: 25
EDDH (HAMBURG) on runway: 23
EDDK (COLOGNE-BONN) on runways: 14L, 32R
EDDL (DUESSELDORF) on runways: 05R, 23L, 23R
EDDM (MUNICH) on ALL runways: 08L, 08R, 26L, 26R
EDDN (NUERNBERG) on runway: 28
EDDP (LEIPZIG-HALLE) on ALL runways: 08L, 08R, 26L, 26R
EDDS (STUTTGART) on ALL runways: 07, 25
EDDT (TEGEL) on runways: 08L, 26R
EDDV (HANNOVER) on runways: 09L, 27R
EDDW (BREMEN) on runways: 09, 27
EDFH (FRANKFURT-HAHN) on runway: 21
EDLV (NIEDERRHEIN) on runway: 27
EDNY (FRIEDRICHSHAFEN) on runway: 24
EDSB (KARLSRUHE/BADEN-BADE) on runway: 21
EDVK (KASSEL-CALDEN) on runway: 27
EFHK (VANTAA) on runway: 22R
EGAA (ALDERGROVE) on runway: 25
EGBB (BIRMINGHAM) on ALL runways: 15, 33
EGCC (MANCHESTER) on runways: 05L, 23R
EGCN (DONCASTER SHEFFIELD) on runway: 20
EGGD (BRISTOL) on runway: 27
EGGP (LIVERPOOL) on runway: 27
EGGW (LUTON) on ALL runways: 08, 26
EGHH (BOURNEMOUTH) on runway: 26
EGHQ (NEWQUAY) on runway: 30
EGKK (GATWICK) on runways: 08R, 26L
EGLL (HEATHROW) on ALL runways: 09L, 09R, 27L, 27R
EGNM (LEEDS BRADFORD) on runway: 32
EGNT (NEWCASTLE) on ALL runways: 07, 25
EGNX (EAST MIDLANDS) on runway: 27
EGPF (GLASGOW) on ALL runways: 05, 23
EGPH (EDINBURGH) on ALL runways: 06, 24
EGSS (STANSTED) on ALL runways: 04, 22
EHAM (SCHIPHOL) on runways: 06, 18C, 18R, 27, 36C, 36R
EHBK (MAASTRICHT-AACHEN) on runway: 21
EIDW (DUBLIN INTL) on runways: 10, 28
EKBI (BILLUND) on ALL runways: 09, 27
EKCH (KASTRUP) on runway: 22L
EKYT (AALBORG) on runway: 26R
ELLX (LUXEMBOURG) on runway: 24
ENGM (GARDERMOEN) on ALL runways: 01L, 01R, 19L, 19R
EPWA (CHOPIN) on runway: 33
ESGG (LANDVETTER) on ALL runways: 03, 21
ESSA (ARLANDA) on runways: 01L, 01R, 19L
ETAR (RAMSTEIN AB) on runway: 26
GMMN (MOHAMMED V INTL) on runways: 35L, 35R
KADW (JOINT BASE ANDREWS) on runways: 01L, 19R
KAFW (FT WORTH ALLIANCE) on runway: 16L
KATL (HARTSFIELD - JACKSON) on runways: 08L, 09R, 10
KAUS (AUSTIN-BERGSTROM INT) on runway: 17L
KBDL (BRADLEY INTL) on runway: 06
KBGR (BANGOR INTL) on runway: 15
KBNA (NASHVILLE INTL) on runways: 02L, 02R
KBOI (BOISE AIR TERMINAL/G) on runway: 10R
KBOS (LOGAN INTL) on runways: 04R, 33L
KBWI (WASHINGTON INTL/MARS) on runway: 10
KCAE (COLUMBIA METRO) on runway: 11
KCLE (CLEVELAND-HOPKINS IN) on runways: 06L, 24R
KCLT (CHARLOTTE/DOUGLAS IN) on runways: 18R, 36C, 36L, 36R
KCVG (CINCINNATI/NORTHERN ) on runways: 36C, 36R
KDAY (COX-DAYTON INTL) on runway: 06L
KDEN (DENVER INTL) on runways: 34L, 34R, 35L, 35R
KDFW (DALLAS-FT WORTH INTL) on runways: 17C, 17L, 18R, 35C, 35R
KDSM (DES MOINES INTL) on runway: 31
KDTW (DETROIT METRO WAYNE ) on runways: 03R, 04L, 04R
KEUG (MAHLON SWEET) on runway: 16R
KEWR (NEWARK LIBERTY INTL) on runways: 04R, 22L
KFAT (FRESNO YOSEMITE INTL) on runway: 29R
KGEG (SPOKANE INTL) on runways: 03, 21
KGSO (PIEDMONT TRIAD INTL) on runway: 05L
KGSP (GREENVILLE SPARTANBU) on runway: 04
KGTF (GREAT FALLS INTL) on runway: 03
KHOU (HOBBY) on runway: 04
KIAD (WASHINGTON DULLES IN) on runways: 01L, 01R, 19C, 19R
KIAH (GEORGE BUSH INTERCON) on runways: 08L, 26L, 26R, 27
KILN (WILMINGTON AIR PARK) on runway: 22R
KIND (INDIANAPOLIS INTL) on runways: 05L, 05R
KJAN (EVERS INTL) on runway: 16L
KJAX (JACKSONVILLE INTL) on runway: 08
KJFK (KENNEDY INTL) on runways: 04R, 22L
KLAX (LOS ANGELES INTL) on runways: 24R, 25L
KLIT (CLINTON NATL/ADAMS) on runway: 22R
KMCI (KANSAS CITY INTL) on runways: 01R, 19R
KMCO (ORLANDO INTL) on runways: 35L, 36R
KMDT (HARRISBURG INTL) on runway: 13
KMEM (MEMPHIS INTL) on runways: 36C, 36L, 36R
KMHT (MANCHESTER) on runway: 35
KMKE (GEN MITCHELL INTL) on runway: 01L
KMSN (DANE CO REGL-TRUAX) on runway: 36
KMSP (MINNEAPOLIS-ST PAUL ) on runways: 12L, 12R, 35
KMSY (ARMSTRONG NEW ORLEAN) on runway: 11
KOAK (METRO OAKLAND INTL) on runway: 30
KOMA (EPPLEY) on runways: 14R, 32R
KONT (ONTARIO INTL) on runway: 26L
KORD (CHICAGO OHARE INTL) on runways: 09L, 10C, 10L, 10R, 27L, 27R, 28C, 28L, 28R
KORH (WORCESTER REGL) on runway: 11
KPDX (PORTLAND INTL) on runway: 10R
KPHL (PHILADELPHIA INTL) on runway: 09R
KPIT (PITTSBURGH INTL) on runways: 10L, 10R
KPVD (GREEN STATE) on runway: 05
KPWM (PORTLAND INTL) on runway: 11
KRDU (RALEIGH-DURHAM INTL) on runway: 23R
KRFD (CHICAGO/ROCKFORD INT) on runway: 07
KRIC (RICHMOND INTL) on runway: 34
KSDF (LOUISVILLE MUHAMMAD ) on runways: 35L, 35R
KSEA (SEATTLE-TACOMA INTL) on runways: 16C, 16L, 16R
KSFO (SAN FRANCISCO INTL) on runway: 28R
KSLC (SALT LAKE CITY INTL) on runways: 16L, 16R, 34L, 34R
KSMF (SACRAMENTO INTL) on runway: 16R
KSTL (ST LOUIS LAMBERT INT) on runways: 11, 12L, 30R
KSWF (NEW YORK STEWART INT) on runway: 09
KTPA (TAMPA INTL) on runway: 01L
LBSF (SOFIA) on runway: 27
LDZA (FRANJO TUDMAN) on runway: 05
LEAS (ASTURIAS) on runway: 29
LEBL (JOSEP TARRADELLAS/EL) on runways: 07L, 07R, 25L, 25R
LEGE (GIRONA) on runway: 20
LEMD (ADOLFO SUAREZ MADRID) on runways: 18L, 18R, 32L, 32R
LEPA (PALMA DE MALLORCA) on runway: 24L
LEVD (VILLANUBLA) on runway: 23
LEVX (VIGO) on runway: 19
LEZG (ZARAGOZA) on runway: 30R
LFBD (MERIGNAC) on runway: 23
LFBL (BELLEGARDE) on runway: 21
LFBO (BLAGNAC) on runway: 14R
LFBP (PAU/PYRENEES) on runway: 31
LFJL (METZ-NANCY/LORRAINE) on runway: 22
LFLC (CLERMONT-FERRAND/AUV) on runway: 26
LFLL (SAINT EXUPERY) on runways: 35L, 35R
LFML (MARSEILLE/PROVENCE) on runway: 13L
LFOB (TILLE) on runway: 12
LFOK (VATRY) on runway: 10
LFPG (CHARLES-DE-GAULLE) on ALL runways: 08L, 08R, 09L, 09R, 26L, 26R, 27L, 27R
LFPO (ORLY) on runways: 06, 24, 25
LFQQ (LESQUIN) on runway: 26
LFRB (BRETAGNE) on runway: 25L
LFRS (NANTES/ATLANTIQUE) on runway: 03
LFSB (BASLE-MULHOUSE) on runway: 15
LFST (ENTZHEIM) on runway: 23
LHBP (LISZT FERENC INTL) on runways: 13L, 13R, 31R
LIMC (MALPENSA) on runways: 35L, 35R
LIME (ORIO AL SERIO) on runway: 28
LIMF (CASELLE) on runway: 36
LIML (LINATE) on runway: 36
LIPE (BORGO PANIGALE) on runway: 12
LIPO (MONTICHIARI) on runway: 32
LIPX (VILLAFRANCA) on runway: 04
LIPZ (TESSERA) on runway: 04R
LIRF (FIUMICINO) on runway: 16R
LJLJ (BRNIK) on runway: 30
LKMT (MOSNOV) on runway: 22
LKPR (RUZYNE) on runway: 24
LOWG (GRAZ) on runway: 35C
LOWK (KLAGENFURT) on runway: 28R
LOWL (LINZ) on runway: 26
LOWS (SALZBURG) on runway: 15
LOWW (SCHWECHAT) on ALL runways: 11, 16, 29, 34
LPPT (LISBON) on runways: 03, 21
LROP (HENRI COANDA) on runways: 08L, 08R
LSGG (GENEVA) on runway: 22
LSZH (ZURICH) on runways: 14, 16
LTAC (ESENBOGA INTL) on runway: 03R
LTBA (ATATURK INTL) on runway: 05
LTFM (ISTANBUL) on runways: 16R, 17L, 34L, 35R
LYBE (NIKOLA TESLA) on runway: 12
LZIB (M.R. STEFANIK) on runway: 31
MMTO (LIC ADOLFO LOPEZ MAT) on runway: 15
NZAA (AUCKLAND INTL) on runway: 23L
OMAA (ABU DHABI INTL) on runways: 13L, 31R
OMDB (DUBAI INTL) on ALL runways: 12L, 12R, 30L, 30R
OMDW (AL MAKTOUM INTL) on runways: 12, 30
OPLA (ALLAMA IQBAL INTL) on runway: 36R
OTBD (DOHA INTL) on runway: 33
OTHH (HAMAD INTL) on ALL runways: 16L, 16R, 34L, 34R
PAFA (FAIRBANKS INTL) on runway: 02L
PANC (STEVENS ANCHORAGE IN) on runway: 07R
RJAA (NARITA INTL) on runway: 16R
RJCC (NEW CHITOSE) on runway: 19R
RJCK (KUSHIRO) on runway: 17
RJFT (KUMAMOTO) on runway: 07
RJGG (CHUBU CENTRAIR INTL) on runway: 36
RJOA (HIROSHIMA) on runway: 10
RJSA (AOMORI) on runway: 24
RJTT (TOKYO HANEDA INTL) on runway: 34R
RKSI (INCHEON INTL) on ALL runways: 15L, 15R, 16, 33L, 33R, 34
RKSS (GIMPO INTL) on runway: 14R
SAEZ (EZEIZA INTL MINISTRO) on runway: 11
SBGR (GUARULHOS-GOV ANDRE ) on runway: 09R
SCEL (ARTURO MERINO BENITE) on runway: 17L
SCIE (CARRIEL SUR INTL) on runway: 02
SCQP (LA ARAUCANIA) on runway: 01
SKBO (EL DORADO INTL) on runway: 13R
SPJC (JORGE CHAVEZ INTL) on runway: 15
UAAA (ALMATY) on runways: 23L, 23R
UACC (NURSULTAN NAZARBAYEV) on ALL runways: 04, 22
UBBB (HEYDAR ALIYEV INTL) on ALL runways: 16, 17, 34, 35
UKBB (BORYSPIL INTL) on runway: 36R
ULLI (PULKOVO) on runways: 10L, 28R
UMMS (MINSK-2) on runway: 13L
URWW (GUMRAK) on runway: 06
UTAA (ASHGABAT) on runways: 12R, 30L
UUDD (DOMODEDOVO) on runway: 14R
UUEE (SHEREMETYEVO) on runways: 06L, 06R, 24C, 24R
UWWW (KURUMOCH) on runway: 15
VECC (NETAJI SUBASH CHANDR) on runway: 01R
VHHH (HONG KONG INTL) on runway: 25R
VIAR (SRI GURU RAM DASS JE) on runway: 34
VIDP (INDIRA GANDHI INTL) on runways: 11, 28, 29
VIJP (JAIPUR) on runway: 27
VILK (CHAUDHARY CHARAN SIN) on runway: 27
YMML (MELBOURNE INTL) on runway: 16
YPPH (PERTH INTL) on runway: 21
ZBAA (BEIJING CAPITAL) on runway: 36R
ZBAD (DAXING) on runways: 01L, 35L
ZHHH (TIANHE) on runway: 04R
ZSPD (PUDONG) on runway: 34L

Trivia: only about 19% of all airports in the database have some ILS at all and only about 9% of them have a Cat. III ILS:

And this is the geographic distribution:

Map generated by the Great Circle Mapper


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How do I calculate the wind angle relative to the aircraft's heading?
If I want to calculate the wind angle relative to the aicraft's heading, I use TAS and not IAS, right?
I want to calculate the relative wind angle to the aircraft. I have this information to work with: GS, IAS, TAS, Heading and GPS direction. I wonder if I can just calculate the ground vector (ground speed and direction) minus air vector (TAS and heading)?

Does this answer your question? How to calculate the real Ground Speed from True Air Speed? You can rearrange the formula in the answers to find your wind speed and angle.

Does this question help? It seems to be the same.

Yes, sort of. Thank you


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Why would an artificial horizon's roll axis be different on ground and in flight?
Sorry, if I'm a bit verbose here, but since I don't understand the problem, I have difficulties to describe it.
I created an artificial horizon using an Adafruit precision 9 DoF sensors and their AHRS SW pack, which is quite sophisticated using Kalman Filters and Covariance matrices for fusion. On my dev table, everything works fine. Roll, pitch, yaw, tilt compensated heading, even if I shake it. I clipped it onto my shaver to simulate vibration, everything OK! Hence, I believe its not a HW or SW problem.
The problem occurs when I mount the device onto my ultra light aircraft. Pitch and Yaw/compass course remain OK, but roll becomes strange. When I turn, the roll axis moves into the right direction, but not enough (say 30° instead of 45) and even if I keep turning at the same bank angle, the roll axis displayed moves back to horizontal. As I said, when I turn the sensor from 0° to 45° on the ground, it rolls from 0 to 45 and stays there!
So the only difference is, IMHO the fact that on my dev table, things are pretty stable, while in the air, the sensor moves at 180 Km/h and in curves there might be some issues from centrifugal forces, which dilute the accelerator values and the Kalman filter tries to correct the Gyro rate by an exorbitated accelerometer value, which are normalized, showing 0.99g when flat on the table.
Any suggestion ?

I think you have it spot on with centrifugal forces. Your filter relies too much on "down" being "which direction is the largest acceleration vector".

That's got to be it.  Your device is being fooled by the same "seat-of-the-pants" sensations that humans experience!

You could consider adding a barometer as an altimeter so your filter can better distinguish between a coordinated turn and constantly accelerating upwards.

Can you tune how much the software trusts the gyros and how much it nudges them towards the gravity vector? You basically need it to trust the gyros much more and nudge them toward gravity much less, basically just enough to correct for rotation of Earth plus a bit of drift.

Yes, its possible. There are several tuning parameters, unfortunately there's nothing said about sensitivity #define QWINITAA_9DOF_GBY_KALMAN  10E-5F    //a_e * a_e terms (increase slows convergence to g but reduces sensitivity to shake)
// linear acceleration and magnetic disturbance time constants
#define FCA_9DOF_GBY_KALMAN 0.5F // linear acceleration decay factority of these.

I'm also concerned, if I should feed the normalized g vector into the filter, or non normaklized. On my dev table I have only 1 g, but when in flight, I have e.g. 2g at 60°bank. I can't get my head around, what the additional acceleration does to the filter and what about, when all the forces are balanced in a coordinated turn. It appears to be a question of radius, because pitch up/down is absolutely fine.

A perfect description of the problem is here: https://www.vectornav.com/resources/attitude-heading-reference-system Tweaking the Kalman Filter to almost ignore the ACC-meter only cures some symptoms, but does not solve the underlying problem of additional dynamic and sustained acceleration over the gravity. The solution must be found in this sentence: If an AHRS receives real-time measurements of the velocity of the system, the sustained dynamic acceleration can be estimated and compensated for in the attitude estimation. But I don't know how to do this.

@hans You should edit your question to narrow it down rather than post in the comments.

Does the AHRS have any facility for incorporating GPS input? That's a very effective way of dealing with this problem, which may otherwise be intractible with low-cost sensors.

Yes, its an EFIS and I have speed (IAS & GPS), altitude, heading ...

The problem
As already pointed out in some of the comments, this is a structural problem of using an IMU-only AHRS unit. This unit cannot distinguish between acceleration due to centrifugal force, and acceleration due to gravitational forces (of earth).
For example imagine that you fly level, and then roll into a coordinated turn. The short-term roll-rotation will be picked up by the gyroscope, however in the coordinated turn itself the AHRS only "sees" a constant acceleration through its local z-axis (because you are in a coordinated turn). The gyroscopes on the other hand, will not see any movement at all. Therefore the filter will (over time) assume level flight. In essence, you cannot distinguish between gravitational forces and centrifugal forces in forward flight with the accelerometer alone.
Ways to solve this problem
I am aware of two ways of fixing this problem:

Buy a good gyroscope: If you buy a very good gyroscope, you can simply use its measurements and completly omit the accelerometer. However even good MEMS Gyroscopes still have considerable drift (typically you will notice an roll-angle drift after a couple of minutes). If you are willing to spend your life savings (I belive the price tag is 250k$) on a Ring Laser Gyroscope, you can also solve your problem. Fun fact: A couple of flat earthers bough one of these devices and ultimatively measured the earths rotation...

If you are on a Budget however, it may be cheaper (and more reliable) to give your algorithm some sort of velocity feedback. Typically, this is either a GPS unit (which not only produce a measurement of position, but also a velocity measurement), or a velocity measurement based on a pitot tube. With this measurement available, the centrifugal force can be calculated and be accounted for.

Implementation
How can you implement this in software? Well either you take existing projects from any of the common flight controllers like Ardupilot, or betaflight and adapt these to your needs (not knowing your hardware, I cannot tell you how labor-intensive this will be). Or you try to program your own estimation unit based on your IMU and velocity sensor. Before you try to figure out everything by yourself, I would recommend to first take a look at existing Software, which already implements everything necessary. In a nutshell, you just have to program a relatively simple Kalman filter based on the known equations of motion of a 6-DoF point which also estimates the gyro offsets. A very good example of how such a filter is designed can be found on the PX4 project (yet another flight control stack), which details how their Kalman filter is built up. One (open access paper) detailing such an implementation can be found here. I would regard this as the state of the art, and how one would commonly address this problem. The block diagram is displayed here:

Another implementation hinging on a simpler complementary filter, is described in this paper. Based on some minor assumptions it removes the centrifugal force via the airspeed, and uses the centrifugal-force-free acceleration as an input to a complementary filter. Although the used IMU is very high quality, and no algorithm for bias and drift compensation is used, you might get this to work with some adjustments. The block diagram is quite compact:

Disclaimer: I have no affiliation nor contact with any of the authors of the aforementioned papers. I do not own any of the images displayed here, these are directly taken from the papers.
P.S.: Interestingly enough, I also came across this link which offers some bounty for an open-source software implementation of such an AHRS unit.

Re "The only way to fix this is to give the unit some sort of velocity feedback." -- could the problem be fixed simply by reducing the rate at which the system tries to "adjust" the virtual artificial horizon to align with the apparent gravity vector (g-load vector)?

@quietflyer Yes, but then the gyro is on ist own and victim to its high drift rate. Good calibration would be essential to bring that down but will still spoil the signal after several minutes.

@quietflyer Yes, IF you have a very (very) good gyroscopic sensor. However due to (temperature-dependent) drift and noise of standard MEMS Gyros this would not be possible in this specific case. However if you have access to a military grade (100k$+) gyro, then absolutely. If I am not mistaken, this is the way the ultra-high performance ICBMs of the 50s determined their position.
Huh, Peter beat me to that answer :D.

You do not need to spend your retirement savings on a gyro: This device is good enough to be used on UAVs and costs less than 300 USD. Drift with temperature is compensated with calibration tables and a temp sensor, all in one unit.

As said, b4, I'm on a limited budget. @quiet flyer The Algo using the velocity feedback appears 2b "my solution". Do you have some formulas?@ Peter Kämpf, Ardupilot etc. are extremely complex autopilots. Looking for the GPS based attitude correction is like searching the needle in the hay stack. I was investigating in the GPS/speed-correction method, but I can't get my head around this. I have the tangent velocity, but to calculate the centripetal force I would need the actual radius, for which I need the bank angle. Now if I want to calculate the bank angle, I'm stuck in a vicious circle.

I was actually thinking of something very simple. Assuming that the centripetal force has no components in z and the heading axis, the increase of the resulting g-vector magnitude over 1g could be directly attributed to the centripetal force. Wouldn't it be possible the just correct the y-axis w/ the increased g-vector magnitude y= y*1/ |g| ??

@PeterKämpf still for 300 USD, this unit still drifts with 8°/sqrt(h). Or you spend 150 USD for a low-cost IMU including GPS which does not drift at all and gives you an accurate angle reading at all times. @ hans I will try to find another source for you, which might help you better

@hans I guess the GPS data will only tell the control unit when you fly on a straight path and use that as an opportunity to reset drift. Trying to get the centrifugal acceleration right is near impossible, especially in a dynamic environment. I would compare it to step length detection where the moment when a foot is on the ground is used to reset the signal and kill all drift. For the next step the sensor is on its own but that lasts only a second and drift will not be much in such a short interval.

@hans Don't expect a closed solution but iterate your way to the most probable combination of sensor and GPS readings. You start with the bank angle from your artificial horizon and compare what you would expect to what you have (excess over 1 g, just as you assume). Correct a bit each time step and you should get stable results that lag a bit but should be  useable. Basically what a Kalman filter does, too.

@hans I found a couple of papers which might have what you need. This should detail a couple of ways to implement such an AHRS unit as you specified.

To whom it may concern. Since I have started the question, let me now report the solution. Take it w/ a grain of salt, because it works for a micro light ACFT and nothing else. The problem is sufficiently well described here above, hence I just talk about the solution. Other than on the ground, the accelerometer(ACM) undergoes additional forces in curved flights (mainly centrifugal); hence the solution is eliminating the additional force b4 the ACM is used to correct the Gyro by the means of a Kalman Filter.
I will calculate an example, using v= 160Kts and B=30° Bank. all in [m,Kg,s,rad]
The radius of such a curve calculates [F1]: r=v² / g / tan(B) = 82.3² /9.81/0.577 =1197m.
The centrifugal acc calculates [F2] ac= v²/r = 5.65 m/s
However, since we are looking for the bank angle, we are stuck in a vicious circle, because we need the bank angle for calculating the a.m. formulas! So what is the solution? Well the solution is in the circular velocity, or rate of turn (RoT).
RoT= g * tan(B)/v; in our case 9.81 * 0.577/82.3 = 0.0688 = 3.94°/s. Now the trick! If we know the RoT, we can calculate B by solving the equation to B=arc tan(RoT * v/g). But how do we know our RoT?? Well we just read our Gyro z-Axis! We now substitute in [F1] and [F2] B by the formula above getting: ac= g* tan( arctan(RoT*v/g)) hence ac=RoT * v. V we read from IAS or GPS (there are caveats around it) and RoT from the Gyro z-Axis. Making the proof: reading 160Kts from IAS and 3.94 DPS from Gyro gives us the well known 5.65 m/s acceleration of the centrifugal force. Since the accelerometer measures the gravity, we need to convert the ac (5.65 m/s) into g by dividing it by 9.81 m/s. Hence the additional g-force of the centrifugal force calculates: gc= 5.65/9.81= 0.575g. To finally, we just subtract the 0.575g from the ACM y-axis value before we feed it into the Kalman Filter and by the above magic, the artificial horizon now shows a constant bank angle when flying a curve, good enough for me in an ultra light ACFT.
Yours
hk

Sounds good. Unfortunately, many of the answers you got in this topic were incorrect as they make global assumptions about what a 9DoF sensing package can do. As you have described, in the case of an airplane the AHRS system becomes completely observable, esp. when using magnetometer data as this is independent on the inertial frame. There are many formal papers on this subject, and Bill Premerlani has written excellent application notes which he used in his MatrixPilot software package.

I hate to say it, but this don't answer the question. the question asked is "why X". This is an answer about how to fix the "why" but doesn't explain the "why" part. Please remember, SE is not a discussion forum, but a question and answer exchange. You asked a question, and that question needs to be answered. If your answer is how to fix it, then as a new question "what is a solution for when X is happening."

Disclaimer: I am not familiar with the Adafruit software. My experience is more related to the filter software by Sebastian Madgwick.
MEMS gyros are poor in comparison with state-of-the-art fiber gyros which shows in their level of noise and bias. The result is drift: Random walk from noise plus a steadily increasing error from the integration of the rotation rate bias over time. To compensate, the software will compare the orientation with the direction of gravity and nudge the orientation such that the horizon is perpendicular to gravity. This works nicely on the ground but fails as soon as the sensor is subject to a rotation which will add centrifugal acceleration.
That the roll axis moves initially with the roll movement is due to the fact that with every integration step the Kalman filter will apply only a percentage of the correction suggested by the gravity vector. Over time, this correction will then move the indicated horizon parallel with your wings. This is a bit as if you pull the cage knob of a mechanical gyro but that pulling will only move the roll axis a small fraction each time.
If you have the possibility to change the software, I would suggest to set the gravity correction to zero in the Kalman filter and to carefully calibrate the sensor before each flight. Second, add a button that allows to set the horizon to level so you can reset the horizon when you fly wings level. This is how the old mechanical artificial horizons work, too.
Trying to make the gravity correction conditional on the magnitude of the gravity vector will now run into problems with the noise of the accelerometer. You might have success by lowpass filtering the accelerometer and only when you see more than 1g in the filtered signal will you drive the gain in the Kalman filter to zero.
There are much better sensors around than what Adafruit uses, but they are more expensive. However, when you consider the time you sink into working with them, the better performance might well be worth the price. Maybe half of the cost is caused by factory calibration, but then they come with individual compensation tables which will greatly improve their accuracy.

Two things to note here:

All MEMS accelerometers I have worked with, have to be calibrated as well in order to give half-way good measurements. Typically they do not show 1G on flat-level ground.
If I understand correctly, you propose to use the gyros stand-alone (which is the typical approach for high-quality gyros). This will only work for a couple of seconds, as MEMS Gyros are very noise and drifty. The drift is also dependent on temperature, so that the drift will vary depending on how long (and in which environment) you use the sensor.

@U_flow Correct. The bias scatter is already typically ±20 mg out of the factory and might double with soldering. Good gyros have ±1 dps (degree per second) but with calibration are certainly good for several minutes before errors make the signal unusable. Also, the compass can still be used for correction; however, most filters have just one factor to apply gyro correction which is a combination of compass and accelerometer signals. The old clunkers that Adafruit uses might be quite a bit poorer.

I am on a limited budget and I enjoy building/understanding it on my own. Otherwise I could just go and buy a ready made device for a few 100s bucks. The Adafruit board w/ FXAS21002C is rated at 0.3906 dps zero offset @ +/- 250 dps, which is not soooo bad. Reading my ACC/MAG FXOS8700 I receive 1.01g on my dev table.

@hans The FXAS21002C gyro is no longer in production (see product website). This is a decent unit but more recent ones have better specs (this one here has only 1/8 of the noise). But Adafruit puts the sensor in a neat package, together with open source software which is ideal for getting the basics working. Use it as a first step but not as the end result.

@hans "I enjoy building/understanding it on my own." I hope that this thing isn't going on an actual plane, then. Aviation is such a heavily regulated field for a reason, and if someone dies in a plane crash because of your DIY flight instruments, you're probably going to going to jail.


text:
Why did the pilot in this EC135 crash change the throttle setting after encountering wake turbulence?
I’m confused in this accident why the Eurocopter EC135 pilot decided to manipulate the throttle after encountering wake turbulence - I can’t think of a reason for this. Could someone please explain why a pilot would do that?

I'm not sure anyone except the pilot themselves can talk about their motivation, but hopefully someone can talk to the procedures for dealing with wake turbulence in this type or similar.

It's possible that the pilot didn't decide to disable autothrottle, it could have been inadvertent.

It's the second sentence on the first page of the report:

He inadvertently rolled the throttles to manual, and never restabilized the
engines or main rotor rpm.

Supplemented by (the next sentence):

In addition, he did not understand the reset procedures for the
engine controls (FADEC), and never returned the engines to FADEC control.


text:
How can I calculate the minimum thrust to weight ratio required for a given takeoff distance?
I am building a plane and I have a take-off distance of 50ft, is there a way for me to estimate the thrust-to-weight ratio required for this constraint (even if it was in terms of say wing loading)?

Assuming you know the mass $m$ of the aircraft,  the speed $v_0$ required to take off and the lift and drag associated.
Using basic dynamic and newton's second law you can calculate the average acceleration $a$ required to reach take off speed before the end of your runway:
$$a=\frac{v_0^2}{100\text{ft}}$$
Then using your drag generated at takeoff to be on the safe side
$$\text{Thrust} = m * a + \text{Drag}$$
Implying,
$$\frac{\text{Thrust}}{m}=a+\frac{\text{Drag}}{m}$$


text:
How can I know if the Garmin GTX 345 transponder supports modes A and C?
How can I know if the GTX 345 supports mode A/C?
I did not find a mention in the installation manual the capability of mode A/C.

It's on the spec page: Garmin GTX 345:

Physical dimensions (unit, rack, connectors); for panel mounts, depth is measured from face of instrument panel): 1.65” x 6.30” x
10.07” (42 x 160 x 256 mm)
Display type: Digital
Weight (unit, rack, connectors): 3.1/3.2 lbs (1.41/1.45 kg)
Voltage range: 14/28 VDC (18/20 W Max)
Transmit power: 200 W minimum
Temperature: -40° C to +70° C
Operating altitude: To 55,000 ft (16,800 m)
Cooling input: Not required
Environmental compliance (TSO Approved): DO-160G
Software compliance (TSO Approved): DO-178 Levels B, C, D, E
Hardware compliance (TSO Approved): DO-254 Level C
TSO compliance (Approved): TSO-C88b (w/opt. alt. encoder; TSO-C112e (Class 1, Level 2els; TSO-C154c (Class A1S); TSO-C157a (Class 1);
TSO-C166b (Class A1S); TSO-C195a (Class C1,C2,C3,C4)
Mount type: Panel
Transponder type: Mode A/C, S and ES
Squawk code selection: Push-button
Traffic Information Services (TIS) alerts compatible: Yes

I have one of these units, and I can confirm that it supports A/C, S, ES, and ADS-B.

Thanks , it's possible to disable the mode s/es in this unit?

Aside from turning the transponder off, I have not seen a way to disable individual modes (at least from a pilot perspective).


text:
Can fighter jets set their lights to flash six times?
So last night President Trump was in town at the Grand Rapids Airport in Michigan. I live about 5 miles away directly to the west of the airport. I noticed multiple high and fast flying jets (they were not on my Flightaware app). I would see them flashing 6 times quickly with about a 1-2 second pause in-between. It was very consistent. I had never seen 6 quick flashes from any jet ever. I'm hoping someone can verify which type of (I'm assuming fighter) jet can do that, and why?

Welcome to aviation.SE! This question is closely related, and some answers to it point out that at least some military aircraft are able to use several different lighting patterns.


text:
Is the quickest way to reverse direction by turning horizontally or vertically?
Assume my aircraft is flying with Mach 2 and I want to quickly change my direction of travel 180°.

So for a horizontal turn flight I found the formula: angular velocity = g* sqrt(n²-1) / v
For a looping flight I found the formula: angular velocity = g* (n-1) / v

So for the same load factor n my aircraft should do a faster turn with maneuver number 1. Since my angular velocity is higher.
Are my considerations right?
Also, according to both formulas above the ability to do a quick turn around is (let us neglect velocity) only affected by load factor. So my LIFT FORCE (no matter where it acts on my aircraft) is the limiting factor, nothing else. Is that correct? (And lift force is limited for many other reasons...)
Because I had the considerations: if I let the lift force act far away from the center of gravity, I will get a big lever arm and this way a big moment which should create a higher angular velocity. So lift should not be responsible for a quick turn but the lever arm?

It looks like you have created multiple accounts. Be aware that you won't be able to fully participate to the site if you don't gather enough reputation. It is easier to do so by having one single registered account: https://aviation.stackexchange.com/help/merging-accounts

If yort lift is far from center of gravity, you will turn the attitude very fast but not the velocity or the flight path, i.e. in the extreme case your airplane will fly forward but tail first. I don't think that's what you want.

@user3528438, the plane "will fly forward but tail first"?!

Consider deleting the part about "moment arm".  That is a question about control authority, and contains a significant misconception, while the main thrust of your question seems to be about performance.  Assuming you are not going to end up with the controls at full deflection and still wishing for more performance, control authority does not seem very relevant to your main question.  You could explore the issue of whether generating a strong lift force (G-load) tends to make an aircraft pitch up or down, in another question.

What is "n in your equation?  Please modify question to explain.

How about a maneuver combining horizontal and vertical aspects, something like a chandelle?

I would naturally think a near inverted loop/split S initially which then transitions to a horizontal banked turn at some optimal rate would provide the best turn. Is.imteresting because the duel nature of 180 degrees might mean some performance loss is actually accomplishing the task. Also how does energy matter? Simple change direction vs conserving energy.

I suggest researching energy-maneuverability theory. It was developed by John Boyd and Thomas Christie in the 1960's. Boyd was an AF fighter pilot and your question is an important consideration in fighter combat.

Although, in theory, a loop should yield a better turn rate (see my query posted elsewhere on this board), I believe your problem here is the speed of the aircraft.  At Mach 2 (ca 1500 mph), the diameter of the vertical turn - even at 9g's - is probably going to take you into the stratosphere.  Thus, at Mach 2, your only practical option for changing direction by 180 degrees is a horizontal turn.

The formulae appear correct, as far as they go. But there are some problems with the underlying assumption of the question; specifically, that you can achieve either condition in a steady-state fashion.
Firstly, and most importantly, you can see looking at both formulae, the most significant thing you can do to improve your turn rate (angular velocity) is to slow down. This also has a significant effect on the turn radius as well. Since the scenarios where one cares about maximum performance turn rate often also involve a need to avoid an obstacle (cumulonimbus, cumulogranite, etc.), minimizing the turn radius can be just as important as maximizing turn rate, and both can be accomplished by drastically reducing speed.
Conveniently, one of the things that makes it difficult to compare the two scenarios is the fact that the moment you begin the turn, the increased load factor will cause an increase in drag, which will help reduce the speed. The speed reduction (which may be aided by judicious reduction of power) can dramatically improve turn performance, but this reduction will depend on exactly how that turn is made. It may even involve an increase in speed, if attempting the looping turn by performing a split-S.
Importantly, you are trying to compare apples-to-apples by keeping the load factor identical in both scenarios, but I don't find that a plausible assumption. It's not too hard to maintain a constant load factor during a level turn, but a looping turn is likely going to involve either increasing-then-decreasing, or decreasing-then-increasing load factor, making the assumption of load factor being the same in both scenarios unreasonable. And in either case, the speed will be changing by a large amount, eliminating the possibility of using those formulae in an apples-to-apples manner.
Finally, there is the issue that many planes cannot be safely looped, and even among those that can, you may not be able to initiate a loop (Immelmann or split-S) from cruise speed. You have set the assumption that you are cruising at Mach 2, which seems to be an attempt to address this concern. But it raises new ones: even an airplane capable of traveling at Mach 2, may only be able to fly that speed when at altitude, and at an angle-of-attack close to its critical angle of attack, making an Immelmann loop impractical, if not impossible. Similarly, it does not seem likely that one could safely accomplish a split-S that is initiated at Mach 2. The altitude loss incurred could easily exceed the altitude the airplane is starting the turn at, and even if not, the increased airspeed from Mach 2, as well as the G load required at the bottom of the loop, could easily exceed the airplane's structural limits (or the pilot's!).
The conclusion of your question is particularly confusing:

my LIFT FORCE (no matter where it acts on my aircraft) is the limiting factor, nothing else. Is that correct?

and

lift should not be responsible for a quick turn but the lever arm?

Indeed, during a level turn, with a large enough bank angle, one can improve turn performance at the expense of added drag and reduced speed by pulling on the elevator, i.e. adding nose-up elevator input.
But I'm not sure that's what you're asking. It sounds like maybe you're wondering about using lift to modify the attitude of the airplane. If so, that's not how it works. While it's true (for a conventional airplane configuration) that whether in level flight or not, the pitch of the airplane, controlled by the elevator input, changes around the center of gravity, it's important to keep in mind that the center of gravity in unaccelerated flight is directly below the center of lift, since the elevator has effectively added weight, shifting the CG rearward.
I.e. there's no "lever arm" related to any distance between center of gravity and center of lift.
But more to the point, changing the attitude of the airplane isn't the same as changing the flight direction of the airplane. Taking this to its extreme, you can imagine an airplane that could somehow yaw 180 degrees instantaneously. Such an airplane would not effect a 180 degree turn instantaneously; instead, it would just wind up flying the same direction it had already been going, just backwards.
The bottom line: the formulae you're using do not appear to be amenable to an apples-to-apples comparison, so the academic line of reason doesn't seem resolvable. And in the practical sense, if you're going Mach 2 and actually need a maximum performance turn, one of the first things you need to do is slow down. It is most likely safest and most practical to accomplish this in a level turn, or possibly some combination of bank and climb (e.g. like a chandelle). Either way, it's likely the main limiting factor will be the maximum load factor that the airplane and pilot are capable of sustaining.
I don't think it's possible, given only and based solely on the formulae and conditions stated in your post, to determine whether it's always true that a level turn or either type of looping turn is going to produce the maximum rate of turn, first and foremost because you're never going to keep the velocity term in the formulae constant, but for other reasons as well.


text:
How is an aircraft designed to be longitudinally stable?
How do aircraft designers ensure that a specific aircraft is longitudinally stable? Are there any different considerations for subsonic and transonic aircraft?

Can you maybe tell us what you already know about stability so this doesn't start at square one?  Otherwise this is a bit too broad and is in danger of being closed...

I edited your question to try to make it more specific and answerable. It doesn't really matter what the aircraft models are, so I just removed them. If I changed the question too much then you can always roll back my changes, or edit again to clarify something.

1- Given the aircraft list above, compare the air properties at the cruising altitude using the
International Standard Atmosphere (ISA) and discuss how it influences the aircraft aerodynamic
forces.
2- Compare and contrast the primary/secondary flight controls and lift augmentation devices for
each aircraft.
3- Describe how longitudinal stability is achieved for each type of aircraft.

This is actually a reasonable question, but your comment is out of line, and pertains to your other question.

It seems like a clearer question would actually include the comparison, the edited removal of the aircraft changed it into an unspecific query?

My short answer:

Stability is controlled by moving the center of gravity (CoG).
The handbook should give center of gravity limits. A more forward CoG means a more stable airplane.
Shifting it past the neutral point makes the airplane unstable, so movements away from the trimmed state are accelerated. However, at supersonic speed this airplane will become stable again.
Airplanes with sophisticated computer control can artificially augment stability, so they behave like a stable airplane at all speeds.

For the long answer, let me first clarify terms:
Static stability is the tendency of a system to return to it's old state after being disturbed. Take a pendulum: If you pull it to one side, it will return to the middle. Eventually.
Dynamic stability is the tendency of an oscillating system for the oscillations to die down over time. Take the same pendulum: It will swing from side to side, and  friction will ensure this happens with ever smaller amplitude.
Now we need to add dimensions, all three of them: Pitch, roll and yaw. An airplane can be stable in one dimension and unstable in a different one. I understand your question such that you ask about the static pitch stability (or longitudinal stability) of fighter aircraft.
The Wright Flyer was longitudinally unstable (see here for more). Once aircraft designers learned that aircraft can be made to fly stable, and learned that this is of immense benefit in pilot training, static stability became a requirement for new aircraft. When war in Europe broke out, the British forces were equipped with a superb training aircraft, but it was so stable that it took effort and time to convince it to change course. They were shot down in droves.
From now on, low stability was a prime requirement for fighters and aerobatic aircraft. Static stability is proportional to the control forces (more precisely: To the hinge moment of the respective control surface), so reducing stability gave pilots more response for the same effort. Longitudinal static stability is measured as the relative distance between neutral point (NP) and the center of gravity (CG). See here for more. Longitudinal static stability is achieved by placing the CG ahead of the NP. Shifting the CG back gives you a more responsive airplane, but also one which is more easily disturbed by gusts.
This is the design technique you asked about. Pretty simple, right?
Once you shift the CG aft of the NP, stability is lost and the airplane will increase deviations from the trimmed state. This can be helpful if you want large angle changes, and quickly. An unstable aircraft only needs a small kick and will do the rest of the maneuver all by itself.
This is how it helps in maneuverability. But it is even more helpful to reduce the inertias, especially around the roll axis, for a faster response. That is why all combat aircraft have their engines close to the center.
Of course, negative stability is not acceptable when you need to take your hands off the stick to get a map out or to pee on a long flight. So without computer control, the limit was a CG position near, but not aft of the NP.
With supersonic aircraft, things get more complicated. Now the aircraft operates in two flight regimes, one where lift acts at the quarter chord of the wing and one where it acts at mid-chord. Aircraft with low static stability become very stable in supersonic flight, and the tail surface has to create a high down-force so that the sum of all lift stays where the CG is. Creating lift always incurs a drag penalty, and in supersonic flight it has to be payed twice: One for the excess lift on the wing (which is needed to compensate for the tail's down-force) and one for the down-force on the tail.
Using a flight control computer offers the possibility to allow the pilot to let go of the stick without the aircraft going off course. Now the stick does not command elevator deflection, but pitch rate, and the CG can be moved back from maybe 12% of MAC (mean aerodynamic chord) to -2%. If you compare the wing areas of stable and unstable jets (Jaguar and Mirage F-1 are prime examples), you will see how much is achieved just by going back with the CG by a few percent of wing chord.

Conventional SEPECAT Jaguar and CCV version (picture from Ray Whitford's Fundamentals of Fighter Design). Both configurations have the same airfield and combat performance!
These airplanes are unstable without computer control at subsonic speed. This is no benefit in itself (for better maneuverabiliy it helps more to reduce inertias, as explained above), but it dramatically cuts trim drag at supersonic speed. In supersonic flight such an aircraft is still stable, but much less than one that is also stable at subsonic speed. This means less lift is needed on the wings and less downforce is created on the tail, so the drag of both surfaces is small and their size can be reduced, too, resulting in a virtuous circle of drag savings.

Let us know what grade he gets... ;)


text:
Does North Korea's aircraft registration prefix allow for only 500 aircraft?
In the Wikipedia page about aircraft registration prefixes, we can see that North Korea has P-500 to P-999. Does that mean that it’s only allowed 500 planes? What happens when the registry is all used?
(Oddly enough, I visited that Wikipedia page after reading an article about Star Trek’s starship Enterprise, also on Wikipedia.)

This is for civil, not military, aircraft registration, so 500 might actually be plenty for North Korea.

Even if they don't have that many, I'm not sure DPRK would follow an international designation from an organization they aren't a part of.

@RonBeyer They’re a member of both ITU and ICAO.

Civil aircraft tail numbers almost always follow ITU radio prefixes. North Korea has been allocated six ITU prefixes: HM and P5-P9.
Many countries with consecutive 2-letter prefixes will move the dash so it looks like they have a 1-letter prefix, but they still only use the allowed subset. So in this case, rather than P5-00 to P9-99, they write P-500 to P-999. They could have just as easily chosen P-50000 to P-99999 if they wanted, or gone alphabetic for even more possibilities.
However, in practice North Korea only has a handful of very old civil aircraft. While there is a humanitarian exception for spare parts to keep their airlines safe, the country can’t buy any more planes, which means they don’t need more tail numbers than they’re currently using. Heck, they could probably knock off a digit and still have more than they need!


text:
What is required for an EASA pilot to fly an airplane with retractable gear, flaps and variable pitch prop?
Here is the FAA's complex airplane definition:

A retractable gear (not necessary for a seaplane).
In-flight adjustable flaps; and.
A controllable pitch propeller.

How is this airplane defined under EASA and what is required to fly it? A pilot with EASA PPL is able to act as a PIC with retractable gear and flaps; or flaps and controllable pitch. Can he fly an airplane that has all three elements without any additional ratings or endorsements? Or are there any other requirements to fly this type of airplanes?

Welcome to aviation.SE! This question is related.

Also related

Somehow it is, but I meant if I have EASA PPL, will I be able to fly for example Mooney M20, without any additional training to fly this plane (I mean endorsements etc).

I can't find any equivalent definition for what the FAA defines as a complex aircraft for the purposes of endorsements. EASA defines a complex aircraft completely differently.

“‘complex motor-powered aircraft’ shall mean:
(i) an aeroplane:
with a maximum certificated take-off mass exceeding 5700 kg, or
certificated for a maximum passenger seating configuration of more
than nineteen, or certificated for operation with a minimum crew of at
least two pilots, or equipped with (a) turbojet engine(s) or more than
one turboprop engine, or
(ii) a helicopter certificated:
for a maximum take-off mass exceeding 3175 kg, or for a maximum
passenger seating configuration of more than nine, or for operation
with a minimum crew of at least two pilots, or
(iii) a tilt rotor aircraft;”

Yes, I know that EASA defines a complex aircraft differently, my question was rather if I can fly an airplane with retractable gear, flaps, a controllable pitch propeller without any additional endorsements like FAA requires - AOPA article

For an answer to that its best to hear from an EASA CFI.

BTW, as an EASA pilot, there is nothing to stop you from hiring a US CFI and getting a complex/high performance endorsement in your logbook to allow you to operate such aircraft in the N-registry where legally possible. The air work part of the endorsements are all dual.


text:
How do Airbus and Boeing aircraft handle Dutch roll?
I have some homework about Dutch roll filters. Dutch roll is something that is corrected by yaw damper systems, but I would like to know the different ways Boeing and Airbus deal with the issue of Dutch roll.
Is there a separate yaw damper system or is it part of the wider auto pilot system?

You should tell us what is your current state of research so that we can adapt answers to your knowledge.

This is quite similar to the other question you asked.
From my knowledge as a flight simulator enthusiast I can summarize the following:
Boeing aircraft in the past used to be controlled pretty much direct pilot with cables running through the aircraft to control hydraulic actuator valves that power the flight control surfaces. The rudder is usually augmented with a yaw damper system which measures the yaw rate and roll rate, the rudder input and aileron input can “calculates” the desired rudder deflection to dampen the yaw rate and dutch roll. This can be as simple as performing a weighted sum on the yaw rate, roll rate, rudder input and aileron inputs with some factors that may depend on airspeed. The yaw damper(s) can be turned off with a switch in the overhead panel and are relatively simple in design. Easy to test fully and certify easily.
When the autopilot is on it manipulates the flight controls directly, i.e. moves the yoke with mechanical actuators. Thus, the yaw damper doesn't even have to know about the autopilot state in this case.
On Airbus planes and more modern fly-by-wire Boeing aircraft the flight control computers are fed with the pilot inputs and the computers then send signals to the actuators electronically by wire. The controls laws within these computers can be quite complex and usually also incorporate the autopilot control modes.
With full control over all flight surfaces the computers can manipulate individual control surfaces perfectly to remove any undesired motions. E.g. in the A320 the aileron and elevator computers constantly evaluate the current pitch and roll rate against the target rates. Any deviations (e.g. caused by a yaw rate) are immediately countered by aileron, spoiler or elevator inputs. With that alone the Dutch roll already can no longer exist. The roll is already stopped because of the roll feedback loop.
But it doesn't stop there. The flight augmentation computers receive information about the deflections of ailerons and spoilers for example and then can perform internal flight model computations to figure out how much rudder they need to compensate the adverse yaw for example. Or how much aileron will be needed when to stop the Dutch roll as we add rudder deflection. The computers also take the desired turn rate into account and also have inputs such as the balance indicator to fully coordinate the turn to create a slip free turn with close to no side forces on passengers and pretty much zero Dutch roll.
The flight control systems can be almost arbitrarily complex as you add more and more features into it. E.g. when you have an engine failure the computers could also receive inputs from the engine N1 differences and compute the necessary rudder deflection to prevent any yaw from asymmetric thrust. The A380 even goes as far as to use split ailerons on the opposing side of an engine failure to create artificial drag on one side to increase the counter torque. But it can also use ailerons strategically to dampen any oscillations within the wing to create a smoother ride experience. Now you're not only controlling a rigid aircraft, you start to take wing flex into account.
To answer the second question: The yaw damper can be a separate system with parts like asymmetric thrust compensation or other higher level functions just being turned off in case of a computer failure. This way the yaw damper can be used in a more basic control law even if there are mayor failures in other systems which helps control the aircraft in abnormal situations.
Since the yaw damping itself is sort of the last instance before the rudder actuator it doesn't need to be an integrated part of the wider system but the higher level functions will need to be computed somewhere within the control computers. Both implementations probably exist.
... sorry for the long post :)

Thanks for the edit MarianD :)


text:
When does a pilot ask for landing clearance, and when do they recieve it?
Could a pilot flying directly overhead of the airport gain landing clearance, Could a pilot on the wrong end of runway heading get landing clearance, Or would they require approach instructions, or line up themselves first?

You already asked this question, and received answers here: https://aviation.stackexchange.com/questions/72154/does-a-pilot-need-clearance-to-enter-the-traffic-pattern/72334#72334

Does this answer your question? Does a pilot need clearance to enter the traffic pattern?

You normally never ask for a landing clearance itself. At a VFR airport the controller is mentally sequencing aircraft as they arrive and are cleared into the zone, and gives routing instructions as necessary to make aircraft find their way onto final in the desired sequence with the necessary spacing.  Having already been cleared into the control zone the airport is in, and following routing or reporting instructions provided in your clearance to enter the zone or to start an instrument approach, it'll be provided by the tower without prompting when the tower is satisfied the runway is clear, or will be clear shortly, and you are correctly in position as #1 in the sequence.
The only time you ever ask for a clearance at a controlled airport is if it's unusually late due to controller distractions, and the controller hasn't issued a "cleared to land" by some critical point where you need to know one way or another what the plan is.  At a VFR controlled airport I might speak up while on final at maybe 300 feet or so if I haven't heard from the controller.  On an instrument approach I would speak up if I haven't received a landing clearance shortly after passing the final approach fix.
In both of these cases it's a situation where you are waiting for the clearance, none is forthcoming, and you allow for the possibility the controller is busy with other tasks and keep waiting until you reach a point where it's "ok I gotta know one way or the other; time to speak up".  Sometimes you'll just about to key the mic to ask and the controller will pipe in with "cleared to land" and you can tell from the tone they've caught themselves just in time.

Nit: ICAO rules only allow clearing one plane at a time to guarantee separation, but FAA rules allow multiple clearances under "anticipated separation".

I'm in Canada but taking it to the extreme I remember that kind of thing at Oshkosh.  3 airplanes landing on the same runway at the same time, one going short , one medium, and one long.

@StephenS Actually not 100% true. Look up "Reduced runway separation" and ICAO DOC 4444 section 7.10.2

Your question is quite broad, as flights can be conducted in several different ways and the events leading up to a landing clearance are different.
Generally speaking, ATC will be aware of a flight some time before a landing clearance has to be issued. The actual landing clearance is typically issued somewhere between 5 minutes to 30 seconds before touchdown.
If the flight is operated under instrument flight rules (IFR), ATC will basically handle the flight from start to finish. During the approach, the pilot will be instructed to contact the tower, who will issue a landing clearance when appropriate (the pilot never explicitally requests a landing clearance - everyone knows the flight is inbound to land).
If operating under visual flight rules (VFR) a bit more is left up to the pilot. Normally, a pilot will request to enter the controlled airspace immediately surrounding the airport. The tower will issue instructions regarding approaching the airport and joining the "landing circuit" (the standard route to fly on approach to any runway). Once in the circuit, and when appropriate, tower will issue a landing clearance. Again, the pilot does not explicitally request it, since the pilot would have informed ATC of their intentions when entering the local airspace, so ATC already knows the pilot wants to land.
Could a pilot flying directly overhead get a landing clearance? Sure, but he would be talking to ATC for some time before flying overhead, since that would be inside controlled airspace - which you can't enter without a clearance.
Could a pilot on the wrong end of the runway get a landing clearance? Sure, but, again, the pilot would be talking to ATC long before reaching the runway. The pilot is always free to request another runway for landing than the runway in use ("the wrong end"). Weather, traffic and local regulations permitting, ATC will accommodate such a request.

What if the pilot wants a touch and go or stop and go?

@JamesDavis He will tell ATC during approach, typically on downwind


text:
Do large non-pressurized metal planes have a maximum fatigue cycle?
For example the DC3. The way I understand it, the only thing that "ages" the airframes of DC3 is the landing/takeoff cycles and the accompanied periodic force loading/unloading. Do planes such as this really have a meaningful definition of lifetime of its airframe?
As a side note, is loading/unloading cargos on the floor another kind of cycle too?

Yes they do, and here is why.
Airplanes are made mostly of aluminum rather than steel. It is possible to design a steel part in such a way that it will never succumb to fatigue failure (crack propagation at a stress significantly below the yield stress) but this is not true of aluminum and its alloys. For this reason it is necessary to periodically tear down and inspect aircraft for fatigue cracking of their aluminum structure- in essence, safety is inspected into (aluminum) aircraft because from a design standpoint, it is not possible to design fatigue failures out of their structure.
During that teardown, any part that shows fatigue cracking (or corrosion, or physical damage, etc.) is removed and replaced with a new part that is certifiably fault-free. To some extent this means that a DC-3 with 40,000 hours on it has had so much of its structure replaced over the years that the joke is told that the only part that actually has 40,000 hours on it is the serial number plate.
Flexure of the structure during turbulence in flight is a more significant source of fatigue cycling than cargo loading & unloading cycles.

Note that there is some newer research casting doubt on the concept that some materials (such as structural steels) have a stress level below which they will never fatigue; regardless, these materials are still far more resistant to fatigue than aluminium and its alloys.  (Aluminium and its alloys are, in practically every aspect except weight, terrible structural materials.)

Plane of Theseus?

Yeah baby!! That's a good one!

When you subject aluminum to cyclic loadings, there is a relationship of cycles it takes to crack/ vs material thickness, or structural meat you might say.  If the structure is sufficiently meaty, the number of load cycles to generate cracks become effectively infinite.
Modern airliners have structures carefully designed by analysis to last a certain number of load cycles, then subjected to a fatigue test in a rig to simulate the loads, then whatever cracks turn up have to happen at at least 3 times the number of cycles you are designing for. Put another way, if a crack shows up at cycle X, the life of the structure is set at 1/3 of X.
Airplanes like the DC3 were designed before all this was well understood, and in the slide rule era, so they added lots of meat to be safe, and the result is the 3 has a fatigue life of more or less infinity.
What brings them down, besides accidents, is corrosion in its various forms.  Deal with that and a DC3 will theoretically run forever.
In my book the '3 is the world's greatest engineered transportation device.  I can't think of any other machine that, 85 years after it was designed and 74 years after it was last built, businesses still, in 2019, buy these ancient airframes not to fly around as toys or museum peices, but to put them to work to make money.

Older planes like the DC3 undergo 100 hour and/or annual inspections when used for hire just like other planes, and Airworthiness Directives for maintenance issues are sent out to the fleet as things crop up as well. If the inspections and required maintenance do not show anything, they are signed off to go until the next inspection period.  There are also shops that specialize in tearing down DC3s down to their frame and rebuilding them so they end up like practically a new airplane.
Example https://www.airspacemag.com/flight-today/high-mileage-1053125/
40,000 hours!
So effectively, there is no lifetime to the airframe.


text:
Does a pilot need clearance to enter the traffic pattern?
In one video, I saw a Cessna that got its instructions to enter the pattern along with landing clearance, but I saw another where the pilot just flew in and got clearance somewhere around late-downwind.
Edit: Still confused here, if you need a landing clearance to enter traffic, then why do diagrams like this exist: (Figure 4 indicating the recommended area landing clearance should be given)

And why do you see so many videos on youtube of late landing clearances? And why do I see people get cleared to land when they're on downwind abeam to the numbers if they already have clearance?

Are you asking about a specific country? Regulations and local practices can be quite different in different countries. If you're asking about the US, I suggest you add the tag "faa-regulations".

Can you please link some of the videos you are referring to, that maybe helps to avoid confusion.

@TobiBS I'll See If i can find them.

@Pondlife I was looking for FAA and CAA, But mainly FAA

The US AIM (Aeronautical Information Manual) says:

When necessary, the tower controller will issue clearances or other information for aircraft to generally follow the desired flight path (traffic patterns) when flying in Class B, Class C, and Class D surface areas and the proper taxi routes when operating on the ground. If not otherwise authorized or directed by the tower, pilots of fixed-wing aircraft approaching to land must circle the airport to the left. Pilots approaching to land in a helicopter must avoid the flow of fixed-wing traffic. However, in all instances, an appropriate clearance must be received from the tower before landing.

(AIM 4-3-2-b.)

(AIM Fig 4-3-1)
So it is mandatory to receive a landing clearance, but if traffic flow doesn’t demand it, there is no need to fly the traffic pattern. The controller basically has a lot of freedom here, but the standard is to get instruction to join it, even if this means to join a long final.

I'm very confused " If not otherwise authorized or directed by the tower, pilots of fixed-wing aircraft approaching to land must circle the airport to the left."

Is that implying a holding pattern, or the general left-hand traffic pattern?

As this section talks about airports and only takes into account airspaces around airports (B, C and D), it is about general left-hand traffic patterns. See the graphic below this section in my link.

My apologies, Im asking if "If not otherwise authorized or directed by the tower, pilots of fixed-wing aircraft approaching to land must circle the airport to the left." Is implying the aircraft maintain a HOLDING PATTERN to the left of the airport, I dont mean the direction

Again no, the term pattern here means a traffic pattern as illustrated in https://www.faa.gov/air_traffic/publications/atpubs/aim_html/images/faa_img_e42.jpeg and this is normally flown to the left. For the purpose of the pattern and more details please refer to https://en.wikipedia.org/wiki/Airfield_traffic_pattern

I know what patterns are, But im asking if "pilots of fixed-wing aircraft approaching to land must circle the airport to the left" refers to a traffic pattern or holding pattern

@James Davis it refers to traffic pattern.

At least in my experience, it's much more common NOT to fly a pattern, at least if you're coming from a direction 180 degrees or so from the approach end of the active runway.  Flying a pattern seems to be something you're much more likely to do at an uncontrolled field, in order to avoid conflicts with other traffic.

@jamesqf, flying a complete pattern I agree Is happening seldom enough, but how often do you at least join the pattern on base? That way ATC has you separate from straight in IFR traffic and can make last minute adjustments if necessary. As I have written in my answer, even if you join a long final, that is just the last part of the pattern. However I agree that this depends on local procedures. The field I fly a lot from has multiple flight schools and heavy training traffic, so there you will join downwind in a lot of circumstances. With less traffic it might be different.

@TobiBS: Of course things will differ due to circumstances, but I think a lot of it is just a matter of definition.  For instance, my local field has a north-south runway, and I often approach from the west.  So when I (following ATC instructions) continue west then make a right turn to line up with the runway, am I joining the pattern on base, or just taking the most direct route to the runway?

If separate clearances are required, what are those clearances exactly, And why do I see some people getting landing clearance on late downwind when they're already on the pattern? Is a pattern clearance completely different? What if they don't get landing clearance?

Still confused here, If you need a landing clearance to enter traffic, then why do diagrams like this exist https://i.sstatic.net/kUznA.png and why do you see so many videos on youtube of late landing clearances? And why do I see people get cleared to land when theyre on downwind abeam to the numbers if they already have clearance?

Normally there are three clearances on a towered airport for an arriving aircraft: 1. Entering airspace, implicitly given for C+D by reading your callsign. 2. Entering pattern, implicitly given by either the command to enter a part of the pattern or the landing clearance 3. Landing/Touch and Go/Stop and Go, can only be given explicitly.

Anywhere else I can find more information on this? The manual isn't very definitive. @TobiBS

@TobiBS If ATC Instructs an aircraft to fly straight in, Is the whole traffic clearance part abolished? Would the instruction to fly straight in be given and then a landing clearance on final? The only answers I could get about this were here, Checked for a while on google.

At a controlled airport, you need a clearance to land, and sometimes to enter its airspace (varies by class of airspace and country).  How to enter the pattern is not a clearance, at least if you're VFR.
Depending on other traffic in the area, ATC may give explicit instructions on how to enter the traffic pattern.  If there's no other traffic present (or at least none near enough to cause a conflict), though, ATC may not care how you do it.  Their job is to ensure a "safe, orderly and expeditious flow of traffic," not to dictate every single thing a pilot does.
The diagram you cite shows the standard traffic pattern, which is what pilots use at uncontrolled fields, or at controlled fields if ATC doesn't specifically instruct us to do something different.  Even when ATC does give instructions, it is usually based on the names of the pattern legs, e.g. telling you to enter on base or long final (because that makes the most sense given your position and that of other traffic) rather than on the downwind as usual.

Hi Stephen, Thanks for your response, The pattern image is referring to when atc should ideally give landing clearance (dashed lines)

@JamesDavis In theory, yes. In practice, I've gotten a landing clearance on upwind, on 10 mile final, etc. It all depends on the traffic.

The difference will be controlled and non controlled airspace.
When in controlled airspace you will receive clearance to enter the pattern and proceed to landing.
In uncontrolled airspace you will transmit on guard or airport freq. your position and type aircraft and state your intentions.

Note: This answer assumes that you are in FAA airspace.
There are two aspects about entering a terminal area to land.  First, there is clearance into the terminal area, and secondly, there is clearance to land. Let's look at them separately.
The clearance into the terminal area is dependent on airspace and your flight flan. You do not need a landing clearance to enter the traffic pattern. This is clearance to fly a path in the sky, but is not a clearance to touch anything on the ground. If your terminal area is controlled, you will need to work with ATC to arrange your entry into the traffic pattern.  Depending on your entry geometry, this could be a full rectangular left hand pattern as you depicted, they could just give you a long final, or anything in between.
For further reading about FAA classes of airspace, this is a good reference.
Where clearance into the traffic pattern permits a flight path, landing clearance allows the airplane to touch the ground, but does not provide any clearance for path of flight.  Thus, if the airfield is controlled, you need to receive a landing clearance before wheels touch the ground.  Situationally dependent, you will typically receive landing clearance about when you turn base.  It is controller technique to give you an earlier or later landing clearance.  You may fly a full traffic pattern expecting to receive clearance, and when on short final it is not received, you have to execute a go around.


text:
How long does it take to issue an FAA medical certificate?
How long does it take for the FAA to issue a medical certificate? Exam was 7/23 and haven’t heard anything since.

Normally when you leave the examiner’s office you take a signed medical certificate with you. If that didn’t happen then the AME should have told you that there was a problem that needed to be resolved by the folks in Oklahoma City. Did the AME mention anything about a deferral? Could you provide more information so we can answer your question?

@JScarry AME did not mention a problem, said that we would receive a letter for every step of the process but we have not received anything. No mention of a deferral at all.

Call your AME and ask. What you describe is entirely outside of the realm of normal experience.

I feel like I have seen a similar question recently...

@dalearn This one?

@Pondlife yes.  While related, it’s definitely not a duplicate though like I thought it might be.


text:
What's that rattling noise from parked jets?
While walking around the airport on a windy day I occasionally hear a tingling or rattling noise from the engines of the parked jets. You can see the fans rotating in the breeze. What’s causing the noise? I should add that the aircraft are not in use, just parked with the engines uncovered.

It's fan or compressor blades rattling loosely in their blade roots as the engines windmill in the breeze.  The blades are attached to a hub or disc, and the retaining systems for the blades have to allow for thermal expansion, and also allow for a little bit of sideways compliance as the blades spin around, so they are a loose fit when cold.  Compressor blades are usually in a kind of interlocking socket and fan blades are often mounted on pins that allow a bit of freedom of movement.

Thanks for the words. Sorry for the duplication.


text:
How do I request a touch and go and then remain closed traffic?
When I first contact a tower to request touch-and-go, if I want to remain closed traffic after the touch-and-go, can I say
'...tower, call sign, location, inbound for touch-and-go and remain closed traffic'?
I learned touch-and-go yesterday and I'm a student pilot in the US.

Or say it plural: Somewhere Tower: N12345 inbound with Yankee, for some touch-and-goes.

I would not recommend the use non-standard phraseology such as "some touch and goes". There are plenty of cases where sloppy radio communications has led to incidents or even accidents. If you want to remain in traffic circuit, request closed traffic. This way both you and tower know what to expect.

If you call inbound for touch-and-go, the tower controller will assume you plan to remain in the pattern until you say otherwise because that is the norm.
If you don't intend to stay in the pattern, say your exact intentions, e.g. "inbound touch-and-go, then departing west".

Yes you can request that on your call, generally if you don't the tower will ask how you will terminate/proceed at which point you will request closed traffic.


text:
What is the proper procedure to change VFR altitude when changing heading from east to west?
When you fly from west to east, sometimes your route heads west to avoid obstacles or to clear class B or C airspace.
According to hemispheric rule, let's pretend I selected 7500 feet for VFR to the east. En route to a destination with flight following, when I change heading to the west and the route to the west takes about 30 mins, can I remain the altitude until I get a new instruction from ATC? Or, should I request descent/climb and follow the hemispheric rule?
The destination and the post-take-off route are to the east, but when most of the route is to the west, it makes me confusing to select a proper altitude.

Are you in controlled airspace?

Your mention of class B or C airspace, and Flight Following, makes me think you're talking about conditions in the US. Is that a correct assumption?

Yes, I'm talking about conditions in the US. In this case you don't need to think about class B or C. I'm just wondering the proper procedure when I change heading

Somewhat related

First, your question implies you have flight following.  So there would really be no need to avoid class C or B airspace since ATC would simply fly you through them or make their own decision to ask you to go around, over, or under them.
ATC should know to assign a different altitude when you change from east to west or vice versa, but if they do not, yes, you should request an appropriate altitude for the heading that will keep you in VMC conditions.
Keep in mind, that if you are told to "resume own navigation" or "proceed on course", they are allowing you to change your heading and altitude as you please, so you wouldn't need to ask for special permission to change it, and in that case, just change to an appropriate altitude that will keep you in VMC.  No need to say anything; if ATC decides they don't like what you're doing, they would give you a new instruction.

When I request flight following, if there is two or more altitude I planned en route due to weather or terrain, etc..which altitude should I say? For example, the initial altitude I fly is 5500, from middle point of the route, I'll climb to 7500, and then arrive at destination.

When you request flight following, tell them your current altitude.  If you're climbing, indicate your current altitude you're passing and your target altitude.  If they assign one and you want to change it, you can ask.

ATC can certainly give you instructions if they need to but flight following is usually advisory only. It's good to tell them that you're changing altitude in particular however in most cases you don't need their permission to actually do it. I think that's probably what you intended in your answer, but the second paragraph in particular makes FF sound more 'formal' than it really is. That may be just me though :-)

Remaining clear of Class B airspace without an explicit clearance to enter that airspace is always the responsibility of the pilot operating under VFR, regardless of whether or not he or she is receiving flight following or is otherwise in communication with ATC. When under flight following, ATC may provide one with a clearance into Class B airspace, or may request that the pilot remain clear, but it is still the pilot's responsibility to ensure regulatory compliance.

If you are on VFR Flight Following you usually don’t need to ask permission to change altitudes. The exception would be if you are given an altitude to fly from ATC. For example, last week I was flying west from Corona and approaching Burbank’s airspace. While climbing through 4,000' I was given an altitude restriction of “At or below 5,000'”. ATC had me fly over Burbank’s Class C altitude (4,800') but wanted to keep me below the departing traffic. I could see a big jet pass me and once it did I was told to “resume own navigation”. On my initial call I had indicated that I was going to fly home at 6,500' so I climbed to that altitude. I could fly at any appropriate altitude, e.g. 4,500', 6,500', 8,500' etc. but given how busy the airspace is and the expectation of ATC that I would remain at 6,500' I would not change altitude unless I first arranged to do so with ATC.
On the flight into Corona, at around 15 miles from the airport, I was given instructions to fly at or below 3,000'—presumably to avoid traffic departing Ontario. There was no need to inform ATC that I was leaving 3,000' when I had the airport in sight and began my descent.
On the other hand, once I got past Ventura, the traffic volume was much lower so I wouldn’t necessarily talk to ATC if I wanted to climb to go over a mountain or avoid a cloud.
As a general rule, when you begin your descent to land ATC can figure it out. In many cases the beginning of the descent corresponds with picking up the ATIS. Since ATC likes to know that you have the ATIS I will usually combine the descent and ATIS call in one transmission.
In your specific example, since you will be flying at the wrong altitude for 30 minutes, you should either climb or descend—unless your current altitude was assigned by ATC.
FYI, in SoCal when ATC says  “At or below 5,000'” they really mean “at exactly 5,000'”.

"in SoCal when ATC says “At or below 5,000'” they really mean “at exactly 5,000'”." Maybe it's just me, but if ATC wants to say "maintain 5,000", IMO they should say "maintain 5,000". Alternatively, "5,000 or below, remain outside of Class C" (or whatever the exact phraseology would be) which, in your example, would correspond to effectively a block altitude of 4800-5000, thus making 5000 a convenient, nice, round number. Maybe this is just another one of those idiosyncrasies that differentiate US phraseology from ICAO phraseology...


text:
What type of jack is the flight interphone on transport category aircraft?
Recently became an A&P and part of my job is to be on the ground communicating to the pilots during push backs. Started shopping for a headset and have seen various ones with different adapters and jacks. What size jack would work on the flight interphone  on e.g. a B777?

Doesn't your employer offer the equipment needed to do your job? While headsets admittedly are a somewhat personally tailored item (a model that works well for one person might not work so well for another), I would certainly expect an employer to at least offer a selection of choices, complete with whatever adapters are needed to connect to the aircraft.

Also, even if it's a relatively simple item, I would expect anything connected to an aircraft, and used in a safety-sensitive situation to require a large number of certifications, not just "let's buy something off Amazon...".

The Jacks in the cockpit vary from airline to airline, and the impedance of pilot headsets vary as most military radios use very low impedance and most civilian are high impedance, so a lot of used items need to be checked for exact model numbers. for pilots we commonly have dual plug, 6-pin, and single plug [aka helicopter]
But some headsets have changeable cords.

The jack on every commercial airliner from Boeing and Airbus is a single plug U/174 type (aka helicopter).
That holds true as long as we speak of the external jacks used for the flight interphone and service interphone. In the cockpit this is a different beast. You'll find a lot of variation:

classic two-plug
U/174 (aka helicopter, impedance must be matched, no power to headset)
XLR-5 (passes power to headset, often found in Boeing aircraft)
NeutriCON (passes power to headset, often found in Airbus aircraft)
LEMO (passes power to headset, used mainly by Bose)

What you'll find in the cockpit mainly depends on what the buyer ordered. Boeing standard in their newer aircraft is the classic two-plug and a XLR-5 side by side (e.g. B747-8, B787, not sure about the B777). As an example, the company AvtechTyee supplies their 5775 series jack panel for the B787 First Officers side.


text:
Can I log time in an RV-12 towards a commercial certificate, and is it a TAA?

Can I legally log hours flying RV-12 towards commercial airplane rating?

Does RV-12 qualify as a TAA?

What country are you asking about?

I've added the FAA regulations tag to your question on the assumption that you're asking about the US (since you mentioned TAA). If that's wrong, please edit your question and/or tag it to indicate the correct country. Please always tell us which country or regulations you're asking about.

Assuming that you are asking about the US, there are two parts to your question-total time and Complex/Turbine/TAA time.
As to whether the RV meets the requirements for a TAA that depends on what instrumentation/avionics it has. If it meets the definition, then you can use if for the training part of the aeronautical experience.

§61.129   Aeronautical experience.
(ii) 10 hours of training in a complex airplane, a turbine-powered
airplane, or a technically advanced airplane (TAA) that meets the
requirements of paragraph (j) of this section, or any combination
thereof. The airplane must be appropriate to land or sea for the
rating sought;

Further down in the reg it tells you what a TAA airplane is:

(j) Technically advanced airplane. Unless otherwise authorized by the
Administrator, a technically advanced airplane must be equipped with
an electronically advanced avionics system that includes the following
installed components:
(1) An electronic Primary Flight Display (PFD) that includes, at a
minimum, an airspeed indicator, turn coordinator, attitude indicator,
heading indicator, altimeter, and vertical speed indicator;
(2) An electronic Multifunction Display (MFD) that includes, at a
minimum, a moving map using Global Positioning System (GPS) navigation
with the aircraft position displayed;
(3) A two axis autopilot integrated with the navigation and heading
guidance system; and
(4) The display elements described in paragraphs (j)(1) and (2) of
this section must be continuously visible.

As for total time, read the regulation. An RV is an airplane so as long as you have at least 50 hours of the 250 in an airplane then you are good. You could do all 250 in the RV if you wanted.

(a) For an airplane single-engine rating. Except as provided in
paragraph (i) of this section, a person who applies for a commercial
pilot certificate with an airplane category and single-engine class
rating must log at least 250 hours of flight time as a pilot that
consists of at least:
(1) 100 hours in powered aircraft, of which 50 hours must be in
airplanes.…

You are no longer required to take the practical test in a complex or TAA airplane, so no matter what instrumentation/avionics it has you can use it for your practical.

One small point on your final comment: you can indeed do a checkride in an RV-12 but it's an experimental aircraft so the DPE has to agree first.

@Pondlife Good point. He would also have to own (or borrow) the aircraft since  expirementals can’t be rented out by flight schools for general training.

A minor point - the "iST" version (i.e. the RV-12iST) is factory built and can have the above mentioned electronic instrumentation. As such, it is not experimental and likely would be a TAA.